A motor grader, also known as a road grader, patrol, or maintainer, is a piece of heavy machinery used to create a smooth, wide, flat surface.[1] Traditionally, the grader is used for road maintenance—its main function is to flatten surfaces before the application of asphalt. Presently, these machines are also commonly used for fine grading, spreading, and earthmoving. They can be used for clearing debris and brush, as well as for snow removal.[2] A variety of attachments convert the motor grader into a more versatile machine, enabling the machine to do things such as dig shallow holes. The attachment of an elevating conveyor enables the machine to take loose material from the trailing end of its blade, elevate it, and cast it into a hauling unit.[3]

In the early years of roadbuilding, graders were pulled by a team of oxen, mules, or horses. The first such grader was invented by J.D. Adams.[4] In 1885, Adams introduced the “Little Wonder”—a small, two-wheel, horse-drawn grader with a blade set at a fixed angle. It was capable of angling its wooden wheels to one side. Closely following this development, all other grader manufacturers began to incorporate the leaning wheel principle.[5] This development led the way for the introduction of the Adams’ Road King in 1896. This model was a four-wheel, all-steel grade with an eight-foot blade, and wheels capable of leaning in either direction. By the early 20th Century, steam tractors, and then crawler tractors, were pulling graders.[6]

The industry’s first self-propelled (motor) grader was developed by the Russell Grader Manufacturing Company in 1919;[7] it was introduced as the Motor Hi-Way Patrol No. 1 in 1920. This model used a modified Allis-Chalmerstractor. Subsequent versions would be modified on tractors by other manufacturers, such as Fordson, Cletrac, and McCormick Deering. Shortly after this development, all manufacturers started to include self-propelled versions of graders in their product lines.[8]Caterpillar purchased Russell Grader Manufacturing in 1928 and, as a result of this acquisition, entered the grader market. The same year, J.D. Adams introduced its first self-propelled grader, known as the No. 10. Over time, larger models were given power controls.

On early machines, grader blades were controlled by hand cranks, racks and pinions, which were primarily operated by wheels in the operator’s station. By the 1920’s, manufacturers began developing power controls. Most of these were powered mechanically; however, some were hydraulic, such as those introduced by Galion and Huber.[9] Only after many decades did manufacturers begin manufacturing hydraulic, rather than mechanical, controls. By 1935, J.D. Adams had introduced an improved mono-frame grader with a blade able to extend sideways for trimming banks and shoulders.[10]

Historically, graders have been integral in surface mining—the largest models are used for these applications. In the 1950s and 1960s, massive motor graders were being manufactured to reclaim spoil piles—excavated topsoils or subsoils that were removed during construction. In addition, these large motor graders were used to maintain roads for the largest off-highway trucks.

Over the past half-century, many grader manufacturers have developed large sized graders to add to their product lines. Large graders do not typically sell in big numbers and when they do, it is for a limited amount of time.[11] The large motor grader trend, however, began with the Galion Iron Works Manufacturing Co.’s production of the T-700 model in 1955. This grader set a size record at the time, weighing in at over 40,000 pounds (18,143 kg), with 190 horsepower.[12] The massive model also included powershift transmission, with a torque-converter-drive. Galion later became a division of Dresser Industries Inc. In 1988, Dresser embarked on a joint venture with Komatsu, whose largest grader to date, the GD825A-2, weighs 58,250 pounds (26,421 kg) and has 280 horsepower.

In 1969, another massive motor grader, the double-articulated Autoblade, was introduced by CMI Corporation. This machine was 40 feet (12 m) long, weighed 65,000 pounds (29,484 kg), and contained a power module at both ends. Each module contained a 225 horsepower diesel engine using hydrostatic power. Each engine drove four wheels, making it an eight wheel drive machine. This model, whose cab could rotate 180 degrees in either direction, was capable of precision grading in paving jobs.

The same year, RayGo Inc introduced the Giant, a grader similar to that of CMI, featuring dual-end power and double-articulation. This machine, however, was 106,000 pounds (48,081 kg), and its diesel engines each had 318 horsepower. The Giant, not a precision machine, was suitable for heavy-duty surface mining applications. Rather than the usual circle-mounted blade, this grader’s moldboard was attached to the central frame. In addition, the cab was suspended over the rear articulated joint, providing the operator with a full view of the blade and front end of the machine. RayGo produced the Giant for several years before being acquired by CMI Corporation in 1985.

In 1975, Dominion Road Machinery (later renamed Champion Road Machinery Ltd.) achieved the world size record for a production model grader with its 80-T model.[13] This model, later to be known as the 100-T, weighed 202,000 pounds (91,626 kg), had a 700 horsepower Cummins engine, and a 24-foot (7.3-m) blade. It was used in surface mining applications to maintain roads for large haulers, and to reclaim large areas of land. This machine was for sale for 14 years, but not many were sold.

Five years later, O&K (Orenstein and Koppel) introduced the G-350, a 90,000-pound (40,823-kg) mining grader. This machine was the biggest motor grader for a brief period.[14] Only 34 units were sold worldwide and production of this model was halted in 1986.

O&K’s G-350 did not remain the world’s largest motor grader for long, as 1980 saw the introduction of the biggest motor grader to date, produced by ACCO.[15] This giant, manufactured for only one year, weighed more than 400,000 pounds (181,437 kg), had 1,700 horsepower, 12 tires, and used a 33-foot (10-m) blade.

The world’s current largest grader is produced by Caterpillar, and is known as the 24H.[16] This machine was introduced in 1996; it weighs 137,000 pounds (62,142 kg) and boasts a 24-foot (7.3-m) moldboard.

Though there have been many companies who have successfully marketed motor graders over the past half-century, none has been more successful than Caterpillar; it is responsible for approximately 40 percent of annual motor grader sales.[17] The company’s first venture into the world of motor graders occurred in 1926 when its two-ton crawler tractor was outfitted with Russell Grader Manufacturing Co.’s Motor Patrol No. 4 grader. Two years later, the Caterpillar tractor known as the Twenty was used in conjunction with the Russell Motor Patrol No. 6.

Due to the success of the products, Caterpillar decided to purchase the Russell Grader Manufacturing Company in August 1928. After the acquisition, the company discontinued all Russell products that did not include Caterpillar tractors. Caterpillar now had access to a line of pull-type graders to match its tractors.

In 1931, the company introduced the Caterpillar Auto Patrol, which was the industry’s first self-propelled, rubber-tired motor grader.[18] The drivetrain and grader were designed as a single unit on this machine; the engine was rear-mounted for balance and increased visibility. The company continued to produce tractor-pulled graders until the following decade, but became focused on this new design for future models. This new addition to the product line was known as the No. 9 Auto Patrol.

The company produced many subsequent models in the following years, including the Diesel Auto Patrol, which later became known as the Diesel No. 11. Most notable, however, was the No. 12, introduced in 1938. This series has been the longest running for Caterpillar, with the machines still in production today.

In 1963, Cat unveiled the No.16, which was the first of its large graders. This machine had 225 horsepower and a 14-foot (4.3-m) blade. Weighing 46,500 pounds (21,092 kg), it was the largest on the market at the time.[19] This model was sold for 10 years before the introduction of the 16G. This improved model included the first articulated frame, a 16-foot (4.9-m) blade, 275 horsepower, and weighed 60,150 pounds (27,284 kg). It remained in production for over 20 years, before being replaced by the 16H in 1995, which included a newly designed cab and an electronically controlled transmission.

Other key introductions into the H-Series graders were the 143H and 163H, which are all-wheel-drive machines, as well as the 24H, which is currently the world’s largest grader—[20]a title previously held by the 16H. The H-Series is Caterpillar’s top-selling line.

Motor graders are equipped with a moveable blade known as a moldboard. In general, standard moldboards range from 10 to 16 feet (3 to 4.9 m), but can be up to 24 feet (7.3 m) wide.[21] Different sized moldboards are often required depending on the job. The largest-ever blade was manufactured by ACCO in 1980 and is no longer in production – it was 33 feet (10 m) wide.[22] Moldboards are normally mounted to the grader in a circle-mounted configuration. The moldboard is attached under the grader’s frame with a ring that can be swiveled vertically to adjust the casting angle of the blade.By adjusting this way, the grader is able to work sideways, enabling it to do jobs such as pulling ditches and sloping banks. The motor grader’s front wheels can be tilted up to 20 degrees so as to balance the machine horizontally when the moldboard is working at a vertical angle.[23]

Each motor grader has one of two types of frames: rigid, or articulated. While most new models are comprised of articulated frames, some manufacturers have not upgraded the rigid models that were common in the 1980s and 1990s; however, relatively few rigid models are available in North America today. An articulated frame is beneficial as it provides great maneuverability and versatility on a wider range of jobs than a rigid-framed motor grader.[24]

There are two main types of articulated motor graders: those with the articulation joint in front of the cab, and those with the articulation joint behind the cab. Arguably, the “behind the cab” configuration enables the grader operator to have better visibility and a clearer view of the moldboard.[25] An example of a grader with the articulation joint behind the cab is the Champion grader. This machine, unlike other models, carries its transmission ahead of the joint, adding weight and additional power to the moldboard.

Smaller motor graders, which are sufficient for many grading jobs, are usually between 80 and 150 horsepower. A grader of this size can be used for work in driveways, some road maintenance, landscaping, and smaller-scale parking lot projects. The benefit of a smaller grader is its maneuverability in tight spaces.[26] Large motor graders are used for similar road maintenance and parking lot projects, but on a larger scale.

While many motor graders today have all-wheel drive systems, some only have front wheel or four-wheel drive. For unpaved areas, all-wheel drive is usually necessary. It is also useful in soft soil, as it increases the ability of the grader to move, as well as increasing the pushing power. For smooth, clear areas, all-wheel drive may not be required.

Motor graders today use one of three types of transmissions: hydrostatic, direct-drive, and torque-converter-drive.[27] While large machines generally use direct-drive or torque-converter-drive, smaller machines tend to be hydrostatically driven. This means that a pump, whose flow is moderated with control valves and tubing, feeds a hydraulic motor to produce continuous power.[28]